Folded cylinder gaseous discharge device



I, H. SLEEPER FQLDED CYLINDER GASEQUS DISCHARGE DEVICE HAVING KEEP-ALIVE ELECTRODE Filed May 23, 1960 2 Sheets-Sheet l INCIDENT POWER 2 *,i v W l2 7 a a :5 r

INVENTOR. 9 HAROLD A. SLEEPER ATTORNEY Sept. 1, I SLEEPER FOLDED CYLINDER GASEOUS DISCHARGE DEVICE HAVING KEEP-ALIVE' ELECTRODE Filed May 23, 1960 2 Sheets-Sheet 2 IFIG. 5

IN V EN TOR. HAROLD A. SLEEPER TTORNEY United States Patent 3,147,450 FOLDED CYHNDER GASEOEE DESQHARGE DEVEQE Harold A. Sleeper, South Groveland, Mass, assignor, by mesne assignments, to Vsrian Associates, Palo Alto, Calif., a corporation of Caiifornia Filed May 23, 1960, Ser. No. 30,922 4 Qlaims. (Cl. 333-13) The present invention relates to microwave transmission control devices of the gaseous discharge type and more particularly to an improved tubular energy sensitive device of the folded cylinder type incorporating means for pre-ionization of an internal gaseous atmosphere.

The embodiment of the invention comprises a new concept in gaseous discharge devices as disclosed in US. Letters Patent No. 2,922,124 and 2,922,131, issued to Ray S. Braden on January 19, 1960 and assigned to the assignee of the present invention. The double-walled cylindrical hermetically sealed envelope provides an intense gaseous discharge upon transmission of high power electro magnetic energy pulses to thereby eifectively switch the high power energy to the common antenna employed in radar systems. The electrical parameters of the folded cylinder configuration are extremely useful and power levels in the order of many megawatts may be handled. The spacing of the cylinder walls is of a critical value and the ionized gas assumes the shape of a relatively thin sheath disposed transversely to the incident power in the conventional hollow pipe rectangular waveguide. With the short diffusion path for the ionized gas molecules to travel a faster recovery time may be realized, as well as lower leakage power and reduced arc loss.

With a resonant window assembly including the folded cylinder type unit mounted as the first element in a trans mit-receive or TR tube, switching at higher power levels than heretofore attainable may be realized. In the conventional TR switching tube configuration, the capacitive and inductive elements are mounted in rectangular guide behind the resonant window assembly. One of the most important characteristics necessary to the proper functioning of the switch in a radar system is the minimum firing power and accompanying spike leakage energy. It is the voltage gradient incident upon the window assembly which must attain a pre-determined threshold value at which a self-sustaining gaseous discharge will be initiated. The higher this value becomes the more energy that may be available to pass through the remaining structure to the sensitive receiver to result in possible crystal burnout. The value of the energy permitted to pass before the discharge is initiated is commonly referred to as spike leakage energy.

In the folded cylinder construction careful control of the mixture of gases employed together with lower fill pressures have assisted to some degree in lowering the value of the minimum firing power. It has been ob served, however, that a small amount of residual ionization within the folded cylinder prior to the main transmitter pulse will enable the gaseous discharge to be initiated at a considerably lower threshold Voltage potential. With the reduction of the minimum firing power value an accompanying reduction in spike leakage follows. Hence in a system operating at high peak power levels a normal minimum firing power of 10 kilowatts would be anticipated. Precautions to avert damage to the receiver would be necessary under such conditions. With a pre-ionized gaseous atmosphere the normal firing power characteristic has been found to be reduced by approximately 30 db to values in the order of watts. The improvement in electrical performance will result in a more useful device capable of protecting the receiver apparatus at exceedingly high power levels.

The primary object of the invention, therefore, is the provision of a gaseous discharge device of the folded cylinder type having a shielded reservoir at one end and providing improved operating characteristics.

A further object of the invention is the provision of a gaseous discharge device of the folded cylinder type having means for the pre-ionization of a gaseous atmosphere incorporated therein.

Other objects, advantages, and features will be apparent after consideration of the following detailed specification and reference to the appended drawings, in which:

PEG. 1 is a perspective view of an illustrative embodiment with a portion of the outer wall of the envelope broken away to disclose internal structure and a portion of the structure shown in phantom to reveal underlying components;

FIG. 2 is a schematic view illustrating the operation of the invention as mounted in rectangular waveguide;

FIG. 3 is a cross-sectional view of the embodiment shown in FIG. 1;

FIG. 4 is an enlarged detailed view of the electrode structure incorporated in the embodiment; and

FIG. 5 is an alternative embodiment of the invention.

Turning now to the drawings, FIGS. 1 and 3 illustrate the embodiment 1 comprising concentrically disposed spaced cylinders 23 and 3 of quartz or glass forming the well-known Dewar flask arrangement with a reservoir 4 defined at one end. While the illustrative embodiment refers to a specific folded cylinder configuration, the invention is not limited to this arrangement and maybe practiced in any double-walled envelope defining an annular chamber over the major portion of the axis of the cylinder. A plate member 5 provides means for support ing the cylinder within the central aperture in alignment with the inner walls of a rectangular waveguide section. Plate 5 mates with a flange disposed at one end of an adjacent waveguide which may house the conventional TR structure. A shield 6 encloses the reservoir end of the cylinder. The details in the mounting of a folded cylinder within the plate member have been omitted since the present invention relates solely to the cylinder itself.

Referring now to FIGS. 3 and 4 one feature of the invention resides in the plural electrodes 7 and 8 extending into the annular chamber 9 between the cylinders 2 and 3 and define a discharge gap 10 between the inner ends thereof. The desirable spacing of the gap in an experimental embodiment for use in L-band radar systems was found to be approximately 0.06 inch. The configuration of the electrode inner ends has been shown as a hook 11, however, any other shape will be satisfactory provided the gap spacing is satisfactory for the pre-ionization of the gas. The electrodes may be assembled in the cylinder by fabricating a subassembly comprising the electrodes 7 and 8 sealed to a dielectric bead. An opening is punctured in the end wall 12 joining the ends of the cylinders 2 and 3 to one another. The subassembly may then be inserted in the opening and a glass to glass seal as at 13 will then hermetically seal the electrodes in the proper position. The complete folded cylinder assembly may then be exhausted and filled with an appropriate ionizable atmosphere selected from the noble gases by means of an exhaust tubulation which is pinched off and sealed as at 14.

The outer ends of electrodes 7 and 8 may be electrically connected to a DC. voltage supply circuit 15 having a range of 500 to 1000 volts through a suitable resistor 16. A microarnmeter 17 monitors the current to provide the appropriate ionization.

One of the important features of the invention resides in the orientation of the electrodes 7 and 8 with respect to the incident high power energy transmitted in the waveguide system as shown in FIG. 2. The gap defined by the electrodes is disposed to face the incident power in order that the pre-ionized gas, shown by the dots in the drawing will permit the gaseous discharge to be initiated at a lower threshold value. t may be noted that the discharge gap may be disposed midway between the broad walls of the associated rectangular waveguide structure. The pres ence of the gap even without the D.C. voltage applied may result in a sharp gradient in incident power which will cause the folded cylinder to fire well in advance of the breakdown potential of a cylinder without such structure.

An alternative embodiment of the invention is shown in FIG. 5 wherein a reservoirless type folded cylinder 29 is mounted within a resonant aperture 21 in plate member 22 with the axis of the cylinder lying within the plane of the plate member. Flexible strips 23 provide for retention of the cylinder within the plate member. In this embodiment, paired electrodes 2-427 define a discharge gap at each end of the cylinder, again exposing the preionization discharge at the furthernrost point radially from the plate member to thereby present a lower threshold value to the high level energy incident upon the cylinder. In certain embodiments, plural discharge gaps may be necessary at each end in a spaced arrangement around the periphery of the cylinder tube.

While a specific embodiment has been illustrated and described, it is understood that many variations and modifications may occur to artisans skilled in the art. The foregoing embodiment is, therefore, to be considered in an exemplary and not in a limiting sense, in accordance with the spirit and scope of the invention as defined in the appended claims.

What is claimed is:

1. A resonant window assembly for microwave transmission control devices associated with hollow-pipe rectangular waveguide structure for propagation of high power electromagnetic energy, said assembly comprising a metallic plate member defining a centrally located rectangular opening, a folded cylinder of a dielectric material enclosing substantially all of said rectangular opening with its axis disposed within the plane of the plate member, said folded cylinder comprising a'plurality of concentrically disposed dielectric cylinders sealed together at one of the outer ends to form a hermetically sealed envelope, an ionizable gaseous atmosphere contained within said envelope, and electrode means for partial ionization disposed adjacent at least one end of said envelope at a point nearest to the incident high power propagated in the waveguide, said electrode means comprising a plui rality of conductive wire members extending into said envelope, with the inner ends thereof oppositely disposed to define a discharge gap and adapted for energization by direct current voltage supply means externally connected to said electrodes.

2. A resonant window assembly according to claim 1, wherein said electrode means are disposed at a point located 90 from the plane of the plate member.

3. In a resonant window assembly for microwave trans mission control devices associated with hollow pipe rectangular waveguide structure for propagation of high power electromagnetic energy having a metallic plate member defining a centrally located opening, a folded cylinder of a dielectric material enclosing substantially all of said opening with its axis disposed within the plane of the plate member, said folded cylinder comprising inner and outer concentrically disposed dielectric cylinders sealed together at one of their outer ends to form a hermetically sealed chamber and spaced apart a short distance to form an annular discharge gap over a major portion of said axis of said cylinders and keep-alive electrode means disposed in said sealed outer ends and extending therethrough into said annular discharge gap and defining a keep-alive discharge gap positioned nearer to said sealed outer ends than to the center of said opening, the improvement comprising a hollow chamber bounded by said cylinders, extending over a minor portion of said axis of said cylinders communicating with said annular discharge gap and forming a reservoir containing an ionizable gaseous atmosphere under reduced pressure therewithin, and a conducting metallic plate member disposed circumferentially about said outer dielectric cylinder along said minor portion of said axis for shielding said reservoir from high power electromagnetic energy, whereby the duration required for deionization of said folded cylinder is prevented from becoming so short that substantial deionization occurs during the period when said high power electromagnetic energy is incident upon said folded cylinder, thereby substantially extending the operational life of said transmission control device.

4. In a resonant window assembly for microwave transmission control devices associated with hollow pipe waveguide structure for propagation of high power electromagnetic energy having a metallic plate member defining a centrally located opening, a folded cylinder of a dielectric material enclosing substantially all of said opening with its axis disposed within the plane of the plate member, said folded cylinder comprising inner and outer concentrically disposed dielectric cylinders sealed together at one of their outer ends to form a hermetically sealed envelope and spaced apart a short distance to form an annular discharge gap over a major portion of said folded cylinder axis, said folded cylinder having a gaseous atmosphere within said annular discharge gap under reduced pressure, said gaseous atmosphere being ionizable by said high power electromagnetic energy whenever said high power electromagnetic energy is incident upon said folded cylinder, the improvement comprising a hollow chamber bounded by said dielectric cylinders and extending over a minor portion of said folded cylinder axis, said hollow chamber forming a reservoir communicating with said annular discharge gap and containing an ionizable gaseous atmosphere under reduced pressure therewithin, and a conducting metallic shield member disposed circumferentially about said outer dielectric cylinder along said minor portion of said folded cylinder axis for shielding said hollow chamber from said high power electromagnetic energy, whereby the recovery time required for deionization of said folded cylinder is prevented from becoming so short that substantial deionization occurs during the period when said high power electromagnetic energy is incident upon said folded cylinder, thereby substantially extending the operational life of said folded cylinder.

References Qited in the file of this patent UNITED STATES PATENTS OTHER REFERENCES Microwave Duplexers, vol. 14 of the Radiation Laboratory Series, McGraw-Hill, 1948, pages 197 to 219.

Alexander and Barrett: Methods of Using Pure Noble Gas in Gas Switching Tubes, Microwave Journal, July 1961, pages to 88. 

1. A RESONANT WINDOW ASSEMBLY FOR MICROWAVE TRANSMISSION CONTROL DEVICES ASSOCIATED WITH HOLLOW-PIPE RECTANGULAR WAVEGUIDE STRUCTURE FOR PROPAGATION OF HIGH POWER ELECTROMAGNETIC ENERGY, SAID ASSEMBLY COMPRISING A METALLIC PLATE MEMBER DEFINING A CENTRALLY LOCATED RECTANGULAR OPENING, A FOLDED CYLINDER OF A DIELECTRIC MATERIAL ENCLOSING SUBSTANTIALLY ALL OF SAID RECTANGULAR OPENING WITH ITS AXIS DISPOSED WITHIN THE PLANE OF THE PLATE MEMBER, SAID FOLDED CYLINDER COMPRISING A PLURALITY OF CONCENTRICALLY DISPOSED DIELECTRIC CYLINDERS SEALED TOGETHER AT ONE OF THE OUTER ENDS TO FORM A HERMETICALLY SEALED ENVELOPE, AN IONIZABLE GASEOUS ATMOSPHERE CONTAINED WITHIN SAID ENVELOPE, AND ELECTRODE MEANS FOR PARTIAL IONIZATION DISPOSED ADJACENT AT LEAST ONE END OF SAID ENVELOPE AT A POINT NEAREST TO THE INCIDENT HIGH POWER PROPAGATED IN THE WAVEGUIDE, SAID ELECTRODE MEANS COMPRISING A PLURALITY OF CONDUCTIVE WIRE MEMBERS EXTENDING INTO SAID ENVELOPE, WITH THE INNER ENDS THEREOF OPPOSITELY DISPOSED TO DEFINE A DISCHARGE GAP AND ADAPTED FOR ENERGIZATION BY DIRECT CURRENT VOLTAGE SUPPLY MEANS EXTERNALLY CONNECTED TO SAID ELECTRODES. 